This invention relates generally to optical devices, and more particularly to lasers formed from photonic band gap structures and sub-wavelength grating structures.
Light has several advantages over the electron. As used herein, xe2x80x9clightxe2x80x9d means not only signals in the spectrum of visible light, but also signals in the full spectrum of frequencies typically handled by optical transmission systems. The speed of light is approximately three orders of magnitude higher, compared to the speed of electrons in semiconductors. Thus, photons of light can theoretically carry information approximately 1,000 times faster than electrons in semiconductors. Moreover, photons are not as strongly interacting as electrons with their environment, which allows photonic devices to dissipate less energy, produce less heat and generate less signal noise compared to electronic devices.
In spite of the numerous advantages of photons, all optical circuits have yet to be commercially available on a large scale. Some hybrid opto-electronic circuits have produced significant improvement over the performance of electronic circuits, but the difficulties in designing a multipurpose optical component analogous to the electronic transistor has severely hindered the development of all optical systems.
It is known that as the periodicity of a medium becomes comparable with the wavelength of electromagnetic waves traveling therethrough, the medium begins to significantly inhibit the wave""s propagation. A photonic band gap (PBG) structure is one type of optical structure that is currently being investigated for certain electromagnetic (EM) wave applications. PBGs are formed from photonic crystals, which are composite periodic structures made up of two different dielectric materials. Both dielectric materials should be nearly transparent to electromagnetic radiation in the frequency range of interest. However, the composite periodic structure may not be transparent to the frequency range of interest, due to electromagnetic scattering at the interfaces between the two dielectric components. Intervals of prohibited frequencies are called photonic band gaps.
Relying on the subwavelength wave inhibition effect, PBG structures are two or three-dimensional periodic array structures in which the propagation of EM waves may be described by band structure types of dispersion relationships resulting from scattering at the interfaces between the two dielectric components. Waveguide dispersion is the term used to describe the process by which an electromagnetic signal is distorted by virtue of the dependence of its phase and group velocities on the geometric properties of the waveguide. These photonic band gap structures provide electromagnetic analogs to electron-wave behavior in crystals, with electron-wave concepts such as reciprocal space, Brillouin zones, dispersion relations, Bloch wave functions, Van Hove singularities and tunneling having electromagnetic counterparts in a PBG. This has enabled the development of many new and improved types of photonic band gap devices, including devices in which optical modes, spontaneous emission, and zero-point fluctuations are substantially reduced.
PBG structures can also be formed with added local interruptions in an otherwise periodic photonic crystal, thereby generating defect or cavity modes with discrete allowed frequencies within an otherwise forbidden photonic band gap range of frequencies. Generation of an allowed defect state in an otherwise forbidden band gap enables applications such as high-Q resonators or filters.
In the absence of external currents and sources, Maxwell""s equations for a photon in a dielectric waveguide may be represented in the following form:             {              ∇                  xc3x97                      1                          ε              ⁡                              (                r                )                                              ⁢                      ∇            xc3x97                              }        ⁢          H      ⁡              (        r        )              =                    ω        2                    c        2              ⁢          H      ⁡              (        r        )            
where H(r) is the magnetic field of the photon, xcfx89 is its frequency, c is the speed of light and ∈(r) is the macroscopic dielectric function of the waveguide. The solutions H(r) for and xcfx89 are determined completely by the magnitude and symmetry properties of ∈(r). If ∈(r) is perfectly periodic, as in a photonic crystal comprising a dielectric waveguide having a periodic array of features therein, such as a series of holes etched into the waveguide, the solutions to Maxwell""s equation are quantized, characterized by a wavevector k and a band index n. Thus, the periodicity of the waveguide dielectric constant removes degeneracies that would otherwise allow free photon states at the Bragg plane, forming a photonic band gap. The region of all allowed wavevectors is referred to as a Brillouin zone and the collection of all solutions to the above equation is termed a band structure. Thus, in a perfectly periodic photonic crystal, allowed photonic states are quantized, with band gaps having no allowed states between discrete allowed states.
When a periodic array of features, such as holes, is introduced into a waveguide material to form a perfectly periodic photonic crystal, the wavevector k becomes quantized and limited to Π/a, where a is the spatial period of the holes. In addition to putting a limit on wavevector values, the introduction of an array of holes in a waveguide has the effect of folding the dispersion relations (xcfx89n(k)) of the strip waveguide and splitting the lowest-order mode to form two allowable guided modes. The splitting at the Brillouin zone edge is referred to as a band gap. The size of the band gap is determined by the relative dielectric constants of the waveguide material and the material filling the periodic structures, such as air in the case of holes. The larger the difference in relative dielectric constants, the wider the gap.
If a defect is included into an otherwise periodic PBG structure, an allowed photonic state can be created within the band gap. This state is analogous to a defect or impurity state in a semiconductor which introduces an energy level within the semiconductor""s band gap. A defect in the otherwise periodic PBG structure is formed by incorporating a break in the periodicity of the PBG structure. PBG defects can take the form of a spacing variation using constant features, use features having a different size or shape, or use a different material. Introduction of a PBG defect may result in the creation of a resonant wavelength within the band gap.
The resonant wavelength of a PBG structure may be shifted by changing the defect. For example, a PBG structure using a defect in feature spacing can shift the resonant wavelength by altering the length of the defect in feature spacing. Increasing the defect spacing length increases the resonance wavelength to a longer value and also reduces the cavity""s Q. The Q of an optical resonant cavity is its figure of merit, defined as 2Πxc3x97(average energy stored in the resonator)/(energy dissipated per cycle). The higher the reflectivity of the surfaces of an optical resonator, the higher the Q of the resonator and the less energy loss from the desired mode. An increase in defect length results in a corresponding increase in the effective refractive index felt by the resonant mode due to a reduced density of lower refractive index holes in the higher refractive index waveguide material. The increase in effective refractive index of the waveguide material results in the reduction of the frequency of the resonant mode. This reduction enhances the coupling of the resonant mode to the waveguide mode. This increases the cycle average radiation out of the cavity resulting in a lower Q. A reduction in defect spacing length is expected to produce the inverse result.
Alternatively, the hole spacing may be held constant, but a column of holes having a different size compared to the other PBG holes may be used to introduce an allowed photon state within the PBG band gap. For example, a column of holes may be placed in the PBG hole array having a radius greater or less than the nominal hole radius. As a further alternative, a row of PBG holes filled with a material having a refractive index higher or lower than the material filling the other PBG holes may be used to create an allowed photon state within the PBG band gap. Any of the above techniques may be combined.
Referring to FIG. 1(a), an example PBG structure 100 having a spacing defect is shown. Eight substantially cylindrical holes 101-108 are embedded in silicon waveguide 109. Waveguide 109 has a width 113 of 0.47xcexc and thickness 114 of 0.2xcexc, which can be supported by silicon dioxide cladding layer 110. Holes 101-108 shown are cylindrical having a radius (r) of 0.1xcexc. The center to center spacing 111 (denoted as xe2x80x9caxe2x80x9d) between holes 101 and 102 is 0.42xcexc and equivalent to the distance between holes 102 and 103, 103 and 104, 105 and 106, 106 and 107 and 107 and 108. However, the spacing between holes 104 and 105, 112 (denoted as ad), is not equal to 0.42xcexc. Rather this distance 112 is 0.63xcexc, 50% more than the nominal hole spacing (a).
FIG. 1(b) illustrates the spectral response of the PBG structure 100 etched in a silicon waveguide, as shown in FIG. 1(a). The large contrast of dielectric constant between the silicon waveguide (∈Si=12.1) and PBG features filled with air (∈air,=1) creates a correspondingly wide band gap from between approximately 1300 nm to 1700 nm, or nearly 400 nm as shown in FIG. 1(b). A band gap functions as a stop band. A narrow resonance transmission peak centered at approximately 1540 nm results from placing a spacing defect into the PBG hole array which is otherwise comprised of equally spaced holes. The PBG structure shown in FIG. 1(a) has a calculated cavity quality factor Q of approximately 280 at the resonant wavelength.
Apart from the ability to tune the resonant frequency of the PBG, PBGs allow control of the symmetry of the allowed photonic state. The very specific symmetry associated with each photon mode translates into a specific value of orbital angular momentum for each photon mode which can exist in addition to its intrinsic spin angular momentum. The presence of photon orbital angular momentum states in addition to spin angular momentum states can directly impact the selection rules for electronic transition rates.
The flexibility in tuning the symmetry, frequency and localization properties of photons in PBG cavities makes photonic crystals attractive for the design of novel types of devices, such as lasers. In the case of lasers, photonic crystals can be used advantageously to control the rate of spontaneously emitted radiation.
Spontaneous radiation is energy emitted when a quantum mechanical system drops from a higher energy level (xe2x80x9cexcited statexe2x80x9d) to a lower energy level, without a triggering event. This radiation is emitted according to the laws of probability without regard to the simultaneous presence of similar radiation. Upon an atom""s or ion""s fall to the lower energy state, the energy difference between the higher and lower energy states is released primarily in the form of emitted radiation.
The ability to control spontaneous emission is significant for laser devices. The rate at which atoms decay from high energy states depends on coupling between the atom and the photon, and also on the density of electromagnetic modes available for the emitted photon. PBG crystals can be used to control both the coupling between the atom and the photon, and the density of electromagnetic modes available for the emitted photon independently, simply by changing the properties of the PBG defect states.
For example, the coupling between the atom and the photon involves an integral over all space of the initial and final states of the atom, and of the vector-potential associated with the photon. In the case of a photonic crystal, PBGs can be designed with a vector-potential having a specific orbital symmetry. By doing so, transitions that would otherwise be allowed transitions could be made forbidden, and electronic transitions that were previously forbidden could be made allowable by proper selection of the allowed orbital angular momentum states of the defect-state photon. This latter case would be possible if the wavelength of the electron and that of the photon were designed to be of the same order.
In addition to changing the coupling between the atom and the photon, the rate of spontaneous emission could also be affected by changing the density of allowed states. If a non-zero coupling between the atom and the photon is assumed, the xe2x80x9cnaturalxe2x80x9d rate of emission, in free space, is proportional to the free-photon density of states per unit volume, Df, which is given by:       D    f    ≈            1      ω        ⁢          1              λ        3            
where xcfx89 is the frequency of the transition and xcex the wavelength of light. If the medium is a photonic crystal with a photonic bandgap comprising a range of forbidden frequencies including xcfx89, there are no allowed modes to couple to and spontaneous emission is accordingly severely inhibited. Conversely, if the photonic crystal is designed to place an allowed resonant state coincident with a desired frequency xcfx89, the emission rate could be enhanced dramatically by the increase in the density of available appropriate lower energy states.
By coupling an optical transition to the microcavity resonance, the spontaneous emission rate can be enhanced by a factor xcex7 over the spontaneous emission rate with no cavity. The expression for xcex7 is given as:   η  =            Q              4        ⁢                  xe2x80x83                ⁢        π        ⁢                  xe2x80x83                ⁢        V              ⁢                  (                  c          nv                )            3      
where c is the speed of light and v is the optical transition frequency. A large spontaneous emission enhancement could enable the development of devices such as near zero-threshold lasers.
Sub-wavelength structures (SWS) are a second type of optical structure. Grating structures are generally known in the art to provide a method of dispersing incident electromagnetic wave energy. In particular, gratings comprising periodic elements have been used to diffract electromagnetic wave energy, such as light incident on a grating created by periodic slits cut into a given material. When light is incident on the surface of a single diffraction grating, the light may be reflected (or backward diffracted) and/or transmitted (or forward diffracted) at angles that depend upon the periodicity of the grating relative to the wavelength of the incident light and the light""s angle of incidence. By the process of diffraction, electromagnetic waves such as light can be separated into its component wavelengths thereby forming a spectrum that can be observed, photographed, or scanned photoelectrically or thermoelectrically. Diffraction gratings can be used to influence the amplitude, phase, direction, polarization, spectral composition, and energy distribution of a beam of light. Gratings are therefore used in common instruments such as spectroscopes, spectrometers, and spectrographs.
Optical wavelength may be defined as the wavelength of an EM wave in a given material and is equal to the wavelength of the wave in a vacuum divided by the material""s refractive index. As the period of the grating approaches the optical wavelength of the incident radiation, the diffracted orders begin propagating at increasingly larger angles relative the surface normal of the grating. Eventually, as the grating period is reduced and approaches the optical wavelength of the incident radiation, the angle of diffraction approaches 90 degrees, resulting in propagation of the radiation confined to the plane of the grating. This subwavelength condition effectively couples the fields of the incident radiation within the grating structure, a direction transverse to the surface normal of the grating.
An example of the formation and use of a subwavelength grating structure is described in U.S. Pat. No. 6,035,089, by Grann, et. al (xe2x80x9cGrannxe2x80x9d), which is assigned to Lockheed Energy Research Corporation, predecessor to the assignee of the current application. The entire contents of U.S. Pat. No. 6,035,089 are hereby incorporated by reference. Grann describes a single subwavelength grating structure (SWS) that uses periodically spaced high refractive index xe2x80x9cpostsxe2x80x9d embedded in a lower refractive index dielectric waveguide material to form an extremely narrowband resonant reflector.
A subwavelength grating structure which functions as a zeroth order diffraction grating can be represented by an effectively uniform homogeneous material having an effective refractive index (neff). Under particular incident wave configurations, such as a substantially normal incident beam, and certain structural constraints, such as the refractive index of the medium surrounding the grating less than refractive index of the waveguide less than refractive index of the posts, a subwavelength structure may exhibit a resonance anomaly which results in a strong reflected beam over an extremely narrow bandwidth. If the incident radiation is not within the SWS resonant bandwidth, most of the energy of the incident beam will propagate through the grating in the form of a transmitted beam.
This resonance phenomenon occurs when electromagnetic radiation is trapped within the grating material due to total internal reflection. If this trapped radiation is coupled into the resonant mode of the SWS grating, the field will resonate and redirect substantially all of the electromagnetic energy backwards. This resonance effect results in a nearly total reflection of the incident field from the surface, which may be designed to be extremely sensitive to wavelength.
Grann""s embedded grating structure results in minimal sideband reflections. Since Grann""s resonant structure is buried within a waveguide, both the input and output regions of the grating share the same refractive index, resulting in minimal or no Fresnel reflection losses. Thus, reflection losses are minimized permitting operation as an extremely reflective resonant grating.
Reflective gratings may be combined to perform functions that a single reflective grating is incapable of realizing. For example, a Fabry-Perot interferometer may be constructed by combining two flat highly reflective plates. Fabry-Perot plates are generally set parallel to one another and separated by an optical path length equal to an integral number of half wavelengths of a desired wavelength so that electromagnetic waves of a desired wavelength bounces back and forth between the plates multiple times. Optical path length is the physical separation distance between the mirrors multiplied by the refractive index of the waveguide. For a given plate spacing the requirement for constructive interference being an optical path length equal to an integral number of half wavelengths of the incident radiation of a given wavelength can be fulfilled only at particular incident angles, relative to the surface normal of the plates. Therefore, Fabry-Perot interferometers can be used as spectrometers with high resolution as well as optical resonators. Used as a laser resonator, the Fabry-Perot reinforces only electromagnetic radiation of specific wavelengths traveling perpendicular to the mirror surfaces, and its successive reflections and amplifications form an oscillating mode, creating an optical resonator.
Lasers contain an amplifying medium that functions to increase the intensity of the light that passes through it. The amplifying medium may be a solid, liquid or a gas. In a neodymium YAG (Nd:YAG) laser, the amplifying medium is a solid rod of yttrium aluminum garnate (YAG) containing neodymium ions. Another example of a solid state laser is a laser diode. In a laser diode, also known as a diode laser or semiconductor laser, a semiconductor junction is sandwiched between a p-type semiconductor layer and an n-type layer semiconductor layer. In a dye laser, a fluorescent dye is dissolved in a solvent such as methanol. In a helium-neon gas laser, the amplifying medium is a mixture of helium and neon gases.
The factor by which the intensity of the incident radiation is increased by the laser by action of the amplifying medium is known as the gain. The gain is not constant for a particular type of amplifying medium. Gain depends upon the wavelength of the incoming radiation, the length of the amplifying medium and also upon the extent to which the amplifying medium has been energized or xe2x80x9cpumped.xe2x80x9d
If stimulated emission is to predominate to allow lasing, more atoms must reside in a higher energy state compared to a lower energy state. This condition is referred to as a xe2x80x9cpopulation inversionxe2x80x9d and accomplished through pumping the amplifying medium. Population inversion is a necessary condition for laser action to occur. In all cases, it is necessary to set up a population inversion so that stimulated emission occurs more often than absorption for lasing to occur.
There are several methods of pumping an amplifying medium. When the amplifying medium is a solid, pumping is usually achieved by irradiating the amplifying medium with intense radiation. This radiation is absorbed by atoms or ions within the amplifying medium and raises them into higher energy states. Often, the pumping radiation comes from xenon-filled flashtubes that are positioned alongside the amplifying medium. Passing a high voltage electric discharge through the flashtubes causes them to emit an intense flash of white light, some of which is absorbed by the amplifying medium. A laser that is pumped in this way will generally produce a pulsed output.
Pumping an amplifying medium by irradiating it with intense radiation is usually referred to optical pumping. In some cases, the source of the pumping radiation is another laser.
An amplifying medium can be pumped by passing an electrical discharge longitudinally or transversely through the amplifying medium. Lasers may be pumped by an electric discharge to produce either a pulsed output or a continuous output. Various other methods of pumping the amplifying medium in a laser are used. For example, laser diodes are pumped by passing an electric current across the p-n junction.
The laser cavity has several important functions. Following pumping, spontaneous emission of radiation results from excited atoms within the amplifying medium initiating emission of low intensity radiation into the laser cavity. This radiation intensity is increased in intensity by multiple passes through the amplifying medium so that it rapidly builds up into an intense beam. The cavity can also help to ensure that the divergence of the beam is small by limiting cavity modes. Only radiation that travels in a direction closely parallel to the axis of the cavity can undergo multiple reflections at the mirrors and make multiple passes through the amplifying medium. More divergent rays will execute a zig-zag path within the cavity and will generally escape from the cavity.
The laser cavity also improves the spectral purity of the laser beam. Usually, the amplifying medium will amplify radiation within a narrow range of wavelengths. However, within this narrow range, only radiation of particular wavelengths can undergo repeated reflection up and down the cavity. The characteristics that a radiation beam within the cavity must possess in order to undergo repeated reflections define what is referred to as a cavity mode. Radiation which may still be amplified by the amplifying medium but which does not belong to one of these special modes of oscillation is rapidly attenuated and will not be measurably present in the output beam. Thus, optical cavity will only sustain repeated reflections for particular well-defined allowed wavelengths of radiation, and only certain modes for the allowed wavelengths.
Gas lasers provide advantages over lasers which use liquid or solid amplifying mediums. One advantage of gas lasers is that their output power density is roughly inversely proportional to the diameter of the waveguide. As the walls of the cavity begin decreasing in separation distance, conductive cooling of the gas with the cavity walls improves due to more frequent collisions with the cavity walls. This effect allows the use of higher gas pressures which improves laser output power. A second advantage of gas lasers is their low noise operation relative to other types of lasers, such as those which use solid amplifying mediums.
A micro-laser includes an integrated optical resonator formed from a waveguide, a first and a second subwavelength resonant grating in the waveguide and a photonic band gap resonant structure (PBG) in the waveguide. The PBG is positioned between the first and second subwavelength resonant gratings. The micro-laser also includes at least one amplifying medium in the waveguide. In another embodiment of the micro-laser, the PBG has a plurality of holes, and the amplifying medium substantially fills the PBG holes.
The micro-laser waveguide may be selected from the group consisting of Si, Ge, ZnSe, BaF2, CdTe, LiNbO3 and SBN. The micro-laser waveguide may be substantially planar, and further comprise at least one cladding layer positioned adjacent to the planar waveguide. The at least one cladding layer can comprise at least one lower buffer layer positioned under the waveguide and at least one upper buffer layer positioned over the waveguide.
The micro-laser may further comprise a bulk substrate material, wherein the at least one cladding layer is positioned on the bulk substrate material. The bulk substrate material may be selected from the group consisting of silicon, gallium arsenide and indium phosphate. The cladding layers may be selected from the group consisting of glasses, BaF2 and zinc selenide.
The PBG may comprise at least one row of PBG holes having at least one defect therein. The defect can be selected from the group consisting of a spacing defect and a size defect. PBG holes may extend into the cladding layer.
The amplifying medium may comprise at least one gas. The gas can include carbon dioxide. The gas micro-laser may further comprise a reservoir for storing the amplifying medium. The amplifying medium may also comprise a liquid. The liquid may include at least one dye. The amplifying medium may also comprise lasing crystals, including ruby laser, holmium YAG and erbium YAG.
The micro-laser may further comprise a pump for energizing the amplifying medium. The pump can be an optical pump or an electrical pump. The electrical pump may be a RF oscillator, which can be formed on the bulk substrate material.
The pump may be a laser diode. The laser diode can be formed on the bulk substrate material. The pump may also be another laser, such as a UV laser.
The micro-laser may further comprise a pair of electrically conductive discharge electrodes, wherein the electrically conductive discharge electrodes substantially cover the PBG holes and are separated from the waveguide by the buffer layers. The micro-laser may further comprise at least one cladding layer positioned adjacent to the waveguide, a bulk substrate material and an RF oscillator, wherein the RF oscillator is formed on the bulk substrate material and is electrically connected to the electrically conductive discharge electrodes.
Rows of PBG holes may be arranged in linear arrays. Each subwavelength resonant grating structure can comprise a substantially periodic array of SWS features which may be arranged in substantially linear arrays. SWS features and PBG holes may be arranged along arcs having a radius of curvature.
SWS features may be formed from a material having a refractive index higher than that of the material comprising the waveguide and may be selected from the group consisting of Ge, BaF2, LiNbO3, SBN and Si.
The micro-laser may further comprise a bulk substrate material and a heat sink positioned in contact with the bulk substrate material.
The micro-laser may substantially sustain only one propagating mode or sustain substantially at least two propagating modes. The resonator formed by the first and a second subwavelength resonant grating can have a transmission resonance substantially equal to the transmission resonance of the PBG.
A plurality of the micro-lasers may be formed on a bulk substrate material, wherein the bulk substrate material comprises a plurality of die, where the plurality of micro-lasers are positioned on each die. The plurality of lasers may lase at a plurality of wavelengths.
A method for tuning a micro-laser includes the steps of providing a first and second subwavelength resonant grating structure in a waveguide, the first and second subwavelength resonant grating structures in the waveguide having a first resonant transmission wavelength. A photonic band gap resonant structure (PBG) is provided in the waveguide, the PBG positioned between the first and second subwavelength resonant grating structures, the PBG having a second resonant transmission wavelength. At least one amplifying medium may be introduced into the PBG before tuning. At least one of the transmission resonances is tuned to result in the transmission resonances being substantially equal. Preferably, being substantially equal is when a nominal transmission resonance wavelength (xcex) divided by the spread between the PBG transmission resonance wavelength and the first and second subwavelength resonant grating transmission resonance wavelength (xcex) is less than a square root of the product of the PBG Q and the first and second subwavelength resonant grating structure Q. In this context, the nominal transmission resonance wavelength (xcex) may be defined as the arithmetic mean of the PBG resonant wavelength and the resonant wavelength of the resonator formed by the SWS gratings. In the most preferred embodiment, the ratio of the nominal transmission resonance wavelength (xcex) divided by the spread in transmission resonant wavelengths (xcex) is less than xc2xd the square root of the product of the individual resonators. The method for tuning may be at least one selected from the group of electro-optic, photo-refractive, thermal, magneto-optic and tilting.
A method for producing a micro-laser includes the steps of forming at least one cladding layer, forming a waveguide over the at least one cladding layer, providing a first and second subwavelength resonant grating structure in the waveguide, and providing a photonic band gap resonant structure (PBG) in the waveguide. The PBG is positioned between the first and second subwavelength resonant grating structures, the waveguide having at least one amplifying medium therein. The PBG may comprise a plurality of holes, and PBG holes may be filled with at least one amplifying medium. The method may further comprise the steps of providing a bulk substrate material, wherein the at least one cladding layer is formed over the bulk substrate. The cladding layer may comprise at least one lower buffer layer under PBG holes and at least one upper buffer layer over the PBG holes.
The method may further comprise the steps of forming a first electrically conductive film over the at least one lower buffer layer and forming a second electrically conductive film over the at least one upper buffer layer, the electrically conductive films each forming conductive discharge electrodes. The PBG holes can be substantially covered by each of the electrically conductive discharge electrodes. An RF oscillator made be formed on the bulk substrate material, the RF oscillator electrically connected to the electrically conductive discharge electrodes.
A method for producing at least two micro-lasers on a bulk substrate material, the lasers each operable at a lasing wavelength, comprises the steps of providing the bulk substrate material, forming at least one cladding layer over the bulk substrate material, forming a waveguide over the at least one cladding layer, and providing a first and second subwavelength resonant grating structure in the waveguide. A photonic band gap resonant structure (PBG) is provided in the waveguide, the PBG is positioned between the first and second subwavelength resonant grating structure. The waveguide has at least one amplifying medium therein. In an alternate embodiment, the PBG comprises a plurality of holes substantially filled with the amplifying medium.
The lasers formed may be operated at a plurality of different wavelengths. The micro-laser amplifying medium may be at least one gas, and the gas can be stored in a reservoir. The reservoir can be positioned adjacent to the micro-lasers. The at least one cladding layer may comprise at least one lower buffer layer under the PBG holes and at least one upper buffer layer over the PBG holes. The method may further comprise the steps of forming a first electrically conductive film over the at least one lower buffer layer and forming a second electrically conductive film over the at least one upper buffer layer, the electrically conductive films each forming electrically conductive discharge electrodes. The PBG holes may be substantially covered by each of the electrically conductive discharge electrodes.
The micro-laser of the invention has many uses. A method for processing an electromagnetic signal comprises utilizing the micro-laser for laser radar. The laser may also be used for optical signal regeneration. A method for using the low noise coherent light beam produced by the micro-laser comprises directing an output of the micro-laser into another optical waveguide. The other optical waveguide can be a fiber optic waveguide.
The low noise coherent light beam may be modulated. The modulated low noise output may be used for data transfer, such as in communication systems. The modulated low noise output may also be used for optical computing. A micro-laser with a gas amplifying medium may be used for the above listed uses.